Leached fiber bundle and method

ABSTRACT

A mesh ( 36 ) is placed around a bundle ( 32 ) of fused glass fibers. The bundle is then immersed in a leaching bath ( 44 ). The ends of the bundle are protected from the bath fluid by furrules ( 34 ). Some of the glass of the bundle is leached out, so as to provide a flexible fiber bundle.

BACKGROUND

[0001] The present invention relates to leached fiber bundles (LFBs)which are used in endoscopes and for optical signal communications, andmore particularly, to improved methods of producing such LFBs withhigher quality and reliability.

[0002] It has been previously known to produce image conductors orguides for endoscopes or for transmitting optical signals in the form ofLFBs. Such LFBs include a large number of optical fibers, which may bearranged in an ordered array, with each fiber having a small diameter,for example 10-100 microns. The LFBs may be formed by drawing a fiberbundle preform having a number of pre-arranged optic fiber preforms, inthe form of glass rods and/or tubes, together with at least someleachable glass spacers located between or encapsulating each of thedesired optic fiber preforms. The fiber bundle preform is drawn down tothe desired size for the optical fibers, which are fused together withthe leachable glass spacers as they are drawn, with the leachable glassspacers maintaining a space between the individual optic fibers. Inorder to form a flexible image guide, the ends of the fused opticalfiber bundle are protected with a soft, etch resistant coating, and theleachable glass from the spacers is leached from the fused optical fiberbundle, typically using an acid etch bath. Once the leaching process iscomplete, the individual optical fibers in the middle portion of theleached optical fiber bundle are free and allow the LFB to be flexed,while the ends are still held together. Ferrules are then installed onthe ends to protect the ends from damage and maintain the fibers inposition. The flexible middle portion may be placed within a flexibleouter sheath to prevent the individual optical fibers from beingdamaged.

[0003] There are several problems with this prior known process. Due tothe small size of the optic fibers, the individual fibers in the LFB areextremely sensitive to outside surface damage and breakage duringhandling, such as during removal from the etch bath and furtherprocessing, such as the installation of the end ferrules. This createsan additional expense due to the special handling required for suchfurther operations. The optic fibers of the LFB can also suffer fromdamage or breakage during use in the final product or application, forexample in a flexible endoscope, due to friction and abrasion betweenadjacent fibers as the middle, flexible portion of the LFB is flexed.This results in a loss of image definition and degradation oftransmission capability. It would be advantageous to reduce thepossibility of such optical fiber damage during the formation of the LFBand in the subsequent handling and production of the final product inwhich the LFB is utilized. It would also be advantageous to reduceproduction cost and provide a longer useful life for LFBs.

SUMMARY

[0004] Briefly stated, in one aspect the present invention provides amethod of manufacturing a leached fiber bundle, which includes: (a)arranging a plurality of optic fiber preforms and leachable spacers toform a fiber bundle preform; (b) heating and drawing the fiber bundlepreform to obtain a drawn fiber bundle having a desired size of opticfibers within the bundle; (c) polishing the optical ends of the drawnfiber bundle; (d) coating the ends of the drawn fiber bundle with aleaching agent resistant material; (e) leaching material from thespacers from a middle portion of the drawn fiber bundle so thatindividual optic fibers are free in the middle portion to form aflexible leached fiber bundle; (f) applying an anti-friction powder tothe free middle portion of the optic fibers in the leached fiber bundleto reduce abrasion and friction between the optic fibers during flexingof the leached fiber bundle; and (g) applying a sheath over at least themiddle portion of the leached fiber bundle.

[0005] In another aspect, the invention provides a method ofmanufacturing a leached fiber bundle with reduced damage duringproduction by: (a) arranging a plurality of optic fiber preforms andleachable spacers to form a fiber bundle preform; (b) heating anddrawing the fiber bundle preform to obtain a drawn fiber bundle having adesired size of optic fibers within the bundle; (c) installing a ferruleon each of the ends of the drawn fiber bundle; (d) polishing the opticalends of the drawn fiber bundle; (e) coating the ends of the drawn fiberbundle with a leaching agent resistant material; (f) leaching materialfrom the spacers from a middle portion of the drawn fiber bundle so thatthe optic fibers are free in the middle portion to form a flexibleleached fiber bundle, and preferably (g) applying an anti-frictionpowder to the free middle portion of the optic fibers in the leachedfiber bundle to reduce abrasion and friction between the optic fibersduring flexing of the leached fiber bundle; and (h) applying a sheathover at least the middle portion of the leached fiber bundle. Thisreduces the increased cost involved with installing a ferrule on theends of a LFB after it has been etched, and reduces the possibility offiber damage.

[0006] In another aspect, the invention provides a method ofmanufacturing a leached fiber bundle with reduced potential for fiberdamage by: (a) arranging a plurality of optic fiber preforms andleachable spacers to form a fiber bundle preform; (b) heating anddrawing the fiber bundle preform to obtain a drawn fiber bundle having adesired size of optic fibers within the bundle; (c) polishing theoptical ends of the drawn fiber bundle; (d) coating the ends of thedrawn fiber bundle with a leaching agent resistant material; (e)enclosing the drawn fiber bundle with a leaching agent resistant mesh;(f) leaching material from the spacers from a middle portion of thedrawn fiber bundle so that the optic fibers are free in the middleportion to form a flexible leached fiber bundle; and preferably (g)applying an anti-friction powder to the free middle portion of the opticfibers in the leached fiber bundle to reduce abrasion and frictionbetween the optic fibers during flexing of the leached fiber bundle; and(h) applying a sheath over at least the middle portion of the leachedfiber bundle.

[0007] One or more of the above methods can be utilized individually orin combination in order to produce LFBs with lower cost and less damageduring manufacture, as well as higher reliability in the final endproduct.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing summary, as well as the following detaileddescription of the preferred embodiments of the invention will be betterunderstood when read in conjunction with the appended drawings. For thepurpose of illustrating the invention, there are shown in the drawingsembodiments which are presently preferred. It should be understood,however, that the invention is not limited to the precise arrangementsshown.

[0009]FIG. 1 is a cross-sectional view of an optical fiber bundlepreform used to produce the fiber bundle in accordance with the presentinvention.

[0010]FIG. 2 is a schematic elevational view illustrating the drawing ofthe optical fiber bundle preform in order to form a fused optical fiberbundle.

[0011]FIG. 3 is an elevational view of the fused optical fiber bundle inaccordance with the present invention hasting ferrules installed on eachend.

[0012]FIG. 4 is an elevational view similar to FIG. 3 showing the fusedoptical fiber bundle of FIG. 3 wrapped in an etching material resistantmesh.

[0013]FIG. 5 is an elevational view illustrating the leaching of thefused optical fiber bundle to remove the spacer material between theoptic fibers to form a flexible leached fiber bundle.

[0014]FIG. 6 is an elevational view, partially broken away, of theflexible leached fiber bundle with the end ferrule after the leachingprocess.

[0015]FIG. 7 is a cross-sectional view of the flexible area of theleached fiber bundle showing an optional sheathing in accordance withthe present invention taken along line 7-7 in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Certain terminology is used in the following description forconvenience only and is not considered limiting. The terms “a” and “one”are defined as including one or more of the referenced item unlessspecifically noted. The term “array” as used herein is intended toinclude any type of ordered, two-dimensional arrangement of fiber ends,such as for a flexible image bundle.

[0017] The invention relates to a method of manufacturing a leachedfiber bundle 10, a shown in FIG. 6, which is adapted for use as, forexample, an image conductor or guide for endoscopes or for transmissionof optical signals. The leached fiber bundle 10 includes a plurality ofoptic fibers 12 which may be as small as ten microns in diameter orsmaller. As shown in FIG. 7, the leached fiber bundle 10 may be enclosedin a sheathing of protective material 14, which is preferably a flexiblepolymeric material. However, the sheathing 14 is not necessary.

[0018] In order to manufacture the leached fiber bundle 10, a pluralityof optic fiber preforms 20 are preferably arranged in an ordered arrayand spaced apart using leachable spacers 22 to form a fiber bundlepreform 24, as shown in FIG. 1. The optical fiber preforms 20 arepreferably formed from high index glass cores surrounded by a lowerindex cladding material. The optic fiber preforms 20 are preferablyarranged in rectilinear pattern with the leachable spacers 22 being usedto keep the optical fiber preforms 20 spaced apart from one another. Thespacers 22 are preferably tubular as shown, with the optic fiberpreforms 20 being located within the spacers 22. While the optical fiberpreforms 20 and spacers 22 are shown as circular, those skilled in theart will recognize that other shapes could be utilized for the opticfiber preforms 20 and/or the spacers 22. For example, the optic fiberpreforms 20 and the spacers 22 could be rectilinear in order to hold theoptical fiber preforms 20 in a predetermined spacial relation.Alternatively, the spacers 22 could be in the form of separate rodslocated in the spaces between the optic fiber preforms 20.

[0019] The spacers 22 are preferably formed of an acid-soluble material,such as an acid-soluble glass. However, other suitable materials can beutilized. The optic fibers preforms 20 are preferably made of an etchresistant material.

[0020] As shown in FIG. 2, the fiber bundle preform 24 is preferablyheated and drawn in the usual fashion by heating the fiber bundlepreform 22 locally utilizing heaters 30 and pulling on the fiber bundlepreform in the longitudinal direction to obtain a drawn fiber bundle 32having a desired size and/or spacing of the optic fibers 12 within thebundle 32. This is preferably done in a drawing tower. However, otherdrawing arrangements may be utilized depending upon the particularcircumstances.

[0021] The drawn fiber bundle 32 is preferably cut to a desired lengthfor further processing. As shown in FIG. 3, end ferrules 34 arepreferably placed over the ends and bonded and/or crimped in position.The end ferrules 34 and bonding agent are preferably made of an acidetch resistant material, or may be coated with an acid etch resistantmaterial, if desired. Depending upon the particular application, the endferrules 34 may be omitted or installed after leaching of the spacermaterial drawn fiber bundle 32. However, this entails higher costs andhas a greater probability of damaging the optic fibers 12. An advantageof one embodiment of the present invention is to install the ferrules34, which could be required for a particular connector arrangement ormerely as protection for the ends of the leached fiber bundle 10, whilethe drawn fiber bundle 32 is still a single rigid structure in order toprovide for easier handling and less damage to the optic fibers 12.

[0022] As shown in FIG. 4, it is preferred in accordance with anotherembodiment of the invention that a leaching resistant mesh 36 isinstalled over the drawn fiber bundle 32 prior to leaching the leachablematerial of the spacers 22 from the drawn fiber bundle 12. The mesh 36is preferably formed of an acid resistant polymeric material, such aspolyolefine, and may be an open mesh woven tube, net or a mesh fabricmaterial which can be held in place on the drawn fiber bundle 32 viaacid etch resistant straps or bands. The specific size and shape of themesh may be varied based upon the diameter of the optic fibers 12 and/orthe glass material being utilized. The mesh 36 could be formed of awoven fabric having the-desired permeability. The mesh 36 must be openenough to allow free movement of leached material as well as the acidleaching agent therethrough.

[0023] As shown in FIG. 5, the drawn fiber bundle 32 with the protectedends, which may be protected either through coating with an acid etchresistant material or via installation of the etch resistant ferrules34, is placed in a leaching tank 44, which may contain, for examplehydrochloric acid or any other suitable leachant, depending upon thecomposition of the leachable spacers 22. The spacer rod material isleached from a middle portion of the drawn fiber bundle 32 so thatindividual optic fibers 12 are free in the middle portion to form theleached fiber bundle 10.

[0024] After sufficient neutralization and/or rinsing of the leachedfiber bundle 10, the leached fiber bundle 10 is ready for incorporationinto an endoscope or for use as a optical signal transmission cable.

[0025] In accordance with the invention, the mesh 36 helps to preventdamage to the small diameter optic fibers 12 in the middle portion ofthe leached fiber bundle 10. In one aspect of the invention, a sheath,such as the sheath 14 as shown in FIG. 7, is applied over at least aportion of the leached fiber bundle 10 to provide protection for theoptic fibers 12. An anti-friction powder 40, such as TOS-Pearls® whichare available from GE Bayer Silicone or other suitable anti-friction orparting powders such as talcum powder or PTFE powder may be utilized.This anti-friction powder 40 reduces abrasion and friction between theindividual fibers 12 during flexing of the leached fiber bundle 10. Thishelps to prevent premature wear and breakage of the individual fibers inthe leached fiber bundle 1I which lead to degradation and loss of imagesor signals being transmitted through the leached fiber bundle 10.Utilizing the anti-friction powder leads to increased product life ascompared to the prior known bundles.

[0026] Through the use of the methods in accordance with the presentinvention, it is possible to provide higher quality leached fiberbundles 12 with less damage to the individual optic fibers 12 during themanufacturing process. This produces higher yields and less scrapage dueto manufacturing defects, leading to overall reduced production costsdue to less rejects. Additionally, the reliability and life of theleached optic fiber bundle in use can be substantially increased.

[0027] While the preferred embodiments of the invention have beendescribed in detail, the invention is not limited to the specificembodiments described above, which should be considered as merelyexemplary. Further modifications and extensions of the present inventionmay be developed, and all such modifications are deemed to be within thescope of the present invention as defined by the appended claims.

What is claimed is:
 1. Method of manufacturing a leached fiber bundle,comprising: arranging a plurality of optic fiber preforms and leachablespacers to form a fiber bundle preform; heating and drawing the fiberbundle preform to obtain a drawn fiber bundle having a desired size ofoptic fibers within the bundle; coating ends of the drawn fiber bundlewith a leaching agent resistant material; leaching material from thespacers from a middle portion of the drawn fiber bundle so that theoptic fibers in the middle portion are free to form a flexible leachedfiber bundle; applying an anti-friction powder to the free fibers in themiddle portion of the leached fiber bundle to reduce abrasion andfriction between the individual fibers during flexing of the leachedfiber bundle; and applying a sheath over the middle portion of theleached fiber bundle.
 2. The method of claim 1, wherein theanti-friction powder comprises TOS-Pearls.
 3. The method of claim 1,further comprising installing a ferrule on at least one end of the drawnfiber bundle prior to etching.
 4. The method of claim 3, wherein theferrule is resistant to the leaching agent.
 5. The method of claim 1,wherein a leaching agent resistant coating is located over the ferrule.6. The method of claim 1, further comprising installing a leaching agentresistant mesh over the drawn fiber bundle prior to leaching theleachable material from the drawn fiber bundle.
 7. The method of claim6, further comprising applying the sheath over the mesh.
 8. The methodof claim 1, further comprising polishing the ends of the drawn fiberbundle prior to coating with the leaching agent resistant material. 9.Method of manufacturing a leached fiber bundle, comprising: arranging aplurality of optic fiber preforms and leachable spacers to form a fiberbundle preform; heating and drawing the fiber bundle preform to obtain adrawn fiber bundle having a desired size of optic fibers within thebundle; installing a ferrule on each of the ends of the drawn fiberbundle; and leaching material from the spacers from a middle portion ofthe drawn fiber bundle so that the optic fibers are free in the middleportion to form a flexible leached fiber bundle.
 10. The method of claim9, further comprising polishing ends of the drawn fiber bundle prior andcoating the ends with a the leaching agent resistant material prior toleaching.
 11. The method of claim 9, further comprising applying asheath over the middle portion of the leached fiber bundle.
 12. Methodof manufacturing a leached fiber bundle, comprising: arranging aplurality of optic fiber preforms and leachable spacers to form a fiberbundle preform; heating and drawing the fiber bundle preform to obtain adrawn fiber bundle having a desired size of optic fibers within thebundle; coating the ends of the drawn fiber bundle with a leaching agentresistant material; enclosing the drawn fiber bundle with a leachingagent resistant mesh; and leaching material from the spacers from amiddle portion of the drawn fiber bundle so that the optic fibers arefree in the middle portion to form a flelxible leached fiber bundle. 13.The method of claim 12, further comprising polishing ends of the drawnfiber bundle prior and coating the ends with a the leaching agentresistant material prior to leaching.
 14. The method of claim 12,further comprising applying a sheath over the middle portion of theleached fiber bundle.